Traditionally, transistor production requires a highly complex, cost intensive, prolonged process. Today, due to highly developed inkjet technologies, printed transistors overcome these drawbacks and provide fast, low-cost production with high transistor yields. In addition to overcoming the drawbacks of traditional transistors, these printed transistors may be applied to flexible substrates thus allowing them to be implemented in many technologies, such as active matrix flat panel displays, RFID tags, and Smart Cards. However, because printed transistors inherently possess a charge carrier mobility drastically less than traditionally formed transistors, they have not entirely replaced conventional transistors in today's markets.
Charge carrier mobility is defined as electron or hole diffusivity per volt (cm2/V-s) and is a measure of how fast charge moves through a given material when an electric field is applied. High charge carrier mobility in a transistor correlates to higher switching speeds and thus permits a transistor with high charge carrier mobility to be implemented in many applications and technologies. Printed transistors typically possess a charge carrier mobility of only around 0.01 to 1 cm2/V-s, while traditionally formed transistors have charge carrier mobilities of over 100 cm2/V-s.
Materials with higher charge carrier mobility than used in printed transistors typically require annealing. However, the annealing process has not been used for conventional printed transistors. Printing utilizes a flexible substrate, and conventional flexible substrates are not able to withstand the high temperatures utilized in the annealing process. Therefore, conventional printed transistors have been suited only for applications which permit slow switching speeds.
In many applications, multi-terminal electronic devices made from thin-film amorphous/polycrystalline semiconductive material, such as amorphous silicon, copper indium diselenide or cadmium telluride, have high charge carrier mobility. However, such materials typically require annealing, and typical substrates used in printing cannot withstand the high temperatures used in annealing. Therefore, other more expensive processes are utilized to produce such devices.